Method of inhibiting ice melting salts and products for use in ice melting



,Ueits Stews Pm METHOD OF mnmrrnsc ICE MELTlNG SALTS AND rnonucrs FOR USE nv ICE MELTING I George B. Hatch, Allison l'a., assignor, by mesne assignments, to Hagan Chemicals & Controls, Inc., a corporation of Pennsylvania No Drawing. Filed Feb. 28, 1956, Ser. No. 568,192

' 11 Claims. (Cl. 252-70) This invention relates to a method of melting ice and snow and providing vehicular and pedestrian traction thereon in the presence of steel, aluminum, and other In recent years due to the tremendous increase in motor vehicle traffic, these ice-melting salts have found widespreaduse in the melting of ice and snow on streets, roads, bridges and other vehicular roadways. Such materials are completely soluble in water so that no disposal problem exists as in the case of cinders, slag, sand,

I the presence of aluminum and its alloys.

or other purely abrasive materials. These latter materials corrosive to steel, particularly in the dilute solutions en- 1 countered on roadways when these de-icing salts are diluted by snow or rain. Several effective inhibitors have been developed for use with the chlorides, such as the alkali-metal chromates, the alkali-metal phosphates, and certain proprietary mixtures such as Banox, a material sold by Calgon, Incorporated, which-is a mixture of the phosphates and other materials. Corrosion of the underbodies of trucks, passenger cars, etc. through the use of the chlorides as roadway ice-melting salts has been considerably reduced and their use vhas become widespread during the past several years. The inhibiting salts'such as chromates and phosphates do not,-however, appear to reduce the localized, pitting type corrosion which the chlorides produce upon aluminum and its alloys to any satisfactory extent. a 7

Although protection ag t the corrosion of steel by the alkali-metal chlorides can beprevented by these, additives, certain other metals which are used in vehicle construction, Such a m n an it a l ys. n mas.-

nesium and its alloys are still highly susceptible to chloride corrosion. Aluminum and magnesium alloys and alloys of ferrous metals are components of aircraft, railroad cars, buses, trucks, and other vehicles, and it is one object of my invention to minimize corrosion of these metals where they exist together. andare subject to contact with the de-icing salt solution resulting from the melted ice and snow. Aluminum and its alloys are attacked in such a local manner by the chlorides that these salts cannot be safely used where they will be splashed upon the aluminum alloy surface. The inhibiting salts such as chromates and phosphates seem to have no effect to reduce the pitting-type of corrosion which the chlorides cause on aluminum alloys and these mixtures cannot be used where aluminum is encountered:''

I have found that several salts which have a marked depressing action on' the freezing point of water and thereby are useful ice-melting materials, are essentially harmless to aluminum and its alloys. However, these compounds are still quite corrosive to steel and other ferrous alloys. 1 have found that by inhibiting these compounds, they will not appreciably corrode the ferrous metals and at the same time they can be safely used in My discovery is particularly useful in conjunction with the melting of ice and snow on airport runways, bus and truck loading areas, etc. where as has been stated, most of theequipment is constructed of various metals includingboth steel and aluminum.

My preferred ice-melting compounds 'for use where aluminum alone or aluminum and steel are encountered are all relatively inexpensive andrare in plentiful supply. Although these materials are not quite as effective-in de-. pressing the freezing point of water as are the chlorides, they are sufficiently effective in this respect to make them economically feasible. The alkali-metal nitrates such as sodium and potassium nitrate are virtually non-corrosive to aluminum, magnesium, and their alloys and wheninhibited by the use of my preferred corrosion inhibitors,

"can be used safely'where iron, carbon steel, and other ferrous alloys are encountered.

I have found also that the alkali-metal sulfates and ammonium sulfate are effective, particularly the latter salt. Ammonium sulfate per se is only slightly corrosive to aluminum and its alloys but when inhibited by my pre-v ferred materials, it is virtually non-corrosive to aluminum. Steel is badly corroded by ammonium sulfate but when inhibited, the salt can be safely used as a de-icing material in the presence of steel. Ammonium sulfate even when inhibited, however, is somewhat corrosive to magnesium. While somewhat more costly than either the sulfates or the nitrates, urea may also be employed as a de-icing 'salt since it is non-corrosive to aluminum. It is normally quite corrosive-to steel, but when inhibited by my additives, it can be used in the presence of steel with complete safety. a v

To inhibit the corrosivity of the above named icemelting salts, I combine an alkali-metal polyphosphate with a salt of a divalent metal selected from the group consisting of calcium, strontium, and zinc, the combined mixture being in the neighborhood of 10 percent or less by weight of the ice-melting salt with which it is used.

t. I. h t i d t at a m e wt n. 1 wate to 10% by weight or more may be used but adequate protection can be obtained anywhere in the range of 0.1% to 10%, the preferred range being from about 0.5%

to 2.0% by weight.

While I may vary the ratio of components in the inhibitor viz. the polyphosphate and selected divalent metal salt, I have found that optimum results are obtained when I use an amount of divalent mptalsalt whichi's at lehast chemically equivalent to the amount oifpolyphosv pate.

By a chemically equivalent amount of a salt of a divalent metal of this group of elements I mean that amount which will displace the alkali-metal ion from each molecule of alkali-metal phosphate to form .a metal or alkaline earth metal phosphate. 'Forexample, if a chemically equivalent amount of zinc sulfate (ZnSO is added to sodium metaphosphate (NaPO the Na ion is displaced from the molecule of NaPO in accordance with the equation:

ZnSO +2NaPO Na S0 +Zn(PO In Elementary Quantitative Analysis by Willard and Furman, 2d ed., 1935, D. Van Nostrand Co. Inc.', New York, page57, where a section of the text is devoted to precipitation and complex-formation reactions, the authors state that the equivalent is the amount of the substance whichcontains or reacts with one gram atom of a univalentmetal, one-half gram atom of bivalent metal, etc."

It will be seen from the following that using the chemically equivalent weight for my purposes will vary the actual weight ratio between phosphate and divalent metal salt depending upon (a) the phosphate employed and (b) the divalent metal salt employed. For example, if I use 5% by weight of a sodium phosphate glass having a molar ratio of 1Na O to IP 0 the chemical equivalent in weight percent will be as follows for various divalent metal salts:

If sodium tripolyphosphate (Na P O is chosen as the phosphate in the inhibitor, the following weight percentages will be the chemical equivalents of 5% by weight Of N35Pg0w! Percent Calcium sulfate 4.63

Calcium acetate 5.37

Calcium nitrate 5.57 Zinc sulfate 5.48

Zinc acetate 6.23 Strontium acetate 6.96 Strontium nitrate 7.18

I In other words, the ratio of sodium tripolyphosphate to divalent metal salt will vary between 5 to 4.63' and 5 to 1 in en examples. Althou h. the use o a than the chemically equivalent weight of divalent metal salt (as related to the phosphate) will not result in an inoperative mixture, it is preferred to use at least the 5 chemically equivalent weight or more, an excess doing no harm to the anti-corrosion properties of the combination.

In the development of my invention, I have conducted numerous corrosion tests by immersing specimens of the 10 several metals in large beakers containing about 1000 ml. of solution. The following data was obtained from one set of experiments which was conducted for about 5 days:

TABLE I Continuous immersion with mechanical agitation at room temperature 24-8 ALUMINUMVALLOY (2x3 INCH s'rRiPs GOLD R OLLED STEEL (2X3 INCH STRIPS) 5% Rock salt solution 03. 7 5% Urea solution 49; 4 5% Urea solution (inh 3. 3 5% Sodium nitrate solution 101. 7 5% Sodium nitrate solution (inhibited 10. 2

lnhibitor components present in the tie-icing salt solutions in each instance had the following solution concentration:

0.0190? (llalgfin brand glassy sodium phosphate (moi ratio NmO:

g 5= .1: 0.034% Calcium acetate monohydrate.

0.0oo0% Zinc sulfate (36% Zn).

It is evident from a review of the test panels and the data in Table I that rock salt solutions are corrosive to steel and attack aluminum with a pitting-type of attack; urea solutions alone are not corrosive to aluminum but 50 badly corrode steel, as is. the case with sodium nitrate solutions.

While I have shown the useof a glassy sodium phosphate having a molar ratio of 1.1 to' l Na O:P O I may use any molecularly dehydrated alkali-metal phosphate having a molar ratio of alkali metal to phosphorus pentoxide in the range of from about 0.721 to about 2:1. The use of crystalline phosphates such as sodium tripolyphosphate or sodium pyrophosphate is within the scope of my invention, but I prefer the glassy phosphates such as sodium hexametaphosphate or sodium tetraphosphate as they are somewhat more effective.

I may also use the so-called' insoluble" polyphosphates such as sodium or potassium metaphosphate which are solubilized by certain compounds as more fully described in US. Patent No. 2,405,276. If I' use a potassium polyphosphate (insoluble) in a comp osition which contains ammonium or sodium compounds, the potassium phos phate is rendered soluble by the ammonium or sodium ion. Conversely, if I use aninsoluble sodium phosphate in a mixture containing ammonium, or potassium salts, the phosphate is solubilized quite readily.

A second set of experiments using approximately 1000 m1. of solution in large'beaker swas carried outwith 76 the following results being Obtaind? 'rriinum than was the solution of rock salt. i of localized, pitting attack upon the aluminum in the Weight Loss Ice-Melting Agent (mgJdmfi/ Rock salt solution 4.3 (caused severe pitting) 10% Ammonium sulfate solution v 1. 7 10% Ammonium sulfate solution (Inhibited 1. 5 Ammonium sulfate solution 3.1 25% Ammonium sulfate solution (Inhibited 1. 6 25% Ammonium sulfate solution (Inhibited 1. 6.

COLD ROLLE D STEEL (2X3 INCH STRIPS) l Inhibitor components present in the vie-icing salt solution had the following solution concentration:

0.10% Calgon brand glassy sodium phosphate (moi ratio Na O: P305=1.121).

0.05% Calcium sulfate dihydrate. 0.05% Zinc sulfate (36% Zn). Inhibitor components present in the de-icing salt solution had the following solution concentration:

. 0.25% Calgon. 0.125% Calcium sulfate dihydrato.

0.125% Zinc sulfate (36% Zn). 3 Inhibitor components present in the de-icing salt solution had the following solution concentration:

0.25% Calgon. 0.25% Zinc sulfate (36% Zn).

lnsepection of the above data (Table II) establishes the fact that both the inhibited and the. uninhibited ammonium sulfate solutions were less corrosive to alu- The absence ammonium sulfate solutions is an even more significant factor since such localized pitting is the usual cause for aluminum failure in sodium chloride solutions. Furthermore, my inhibitor component markedly reduces the corrosive attack of ammonium sulfate solutions on steel. 'In a 41-day stagnant continuous immersion experiment at room temperature using strips of 24-8 aluminum, a 5% rock salt solution produced a corrosion rate of 0.3

mg./dm. /day vs. a rate of 0.2 mg./dm. /day for a 5% calcium chloride solution. Specimens which were exposed to both solutions were heavily pitted. Inhibited sodium nitrate, on the other hand (5% solution); gave av favorable rate of only 0.03 mg./dm. /day and there was'no evidence of pitting or other localized attack. The inhibited ice-melting composition in this case had a solution concentration of 0.03% by weight of Calgonbrand glassy sodium phosphate, 0.03% calcium sulfate dihydrate, 0.005% zinc sulfate (36% Zn), and the balance of 4.935% sodium nitrate.

In a 5-day stagnant continuous immersion test at room temperature using specimens of cold rolled steel in a 10% solution of ammonium sulfateythecorrosion rate was found to be 27.3 mg./dm. /day whereas inhibited ammonium sulfate solutions were markedly less corrosive as evident from the following data:

the chlorides in this connection but in view of their pitting efiect upon aluminum, I prefer not to employ them.

The actual amount of inhibited ice-melting compound used in practice will obviously depend upon weather conditions, amount and type of ice or snow deposits, etc. I may mix my compositions with cinders, slag, sand, or other abrasive type materials or use them as adjuncts to the abrasives. My preferred mixtures under general conditions for de-icing airport runways should be spread at a rate of 500-1000 lbs. of de-icing material per mile of standard width runway and if used to freezeproof cinders, etc. stored in the weather, I generally use 100-200 pounds per cubic yard of abrasive.

The following examples of preferred mixtures are illustrative of my invention but I do not limit myself thereto as other mixtures which are effective ice-melting compositions are within the scope of my disclosure herein, the preferred range of components being from about 0.1 to about 10% by weight of the inhibitor mixture and from about 99.9% to about by weight of the icemelting salt, viz. ammonium sulfate, sodium nitrate, or

urea.

' EXAMPLE 1 A p Percent Qz Qt 9 Calgon 1 ZnSO (36% Zn) 1 "EXAMPLE 2 NaNO 98' Calgon 1 ZnSO, (36% Zn) V I 0.5 Calcium acetate monohydrate 0.5

EXAMPLE 3 Urea 98 Calgon 1.2 I 21150 (36% Zn) 0.12 Calcium acetate monohydrate 0.78

I EXAMPLE 4 Urea v 97.8 Calgon 1.2 Calcium acetate monohydrate 1.0

EXAMPLE 5 NaNO 98 Calgon 1.2 ZnSO (36% Zn) 0.12 Calcium acetate monohydrate 0.78

EXAMPLE 6 NaNO Calgon 0.9 ZnSO (36% Zn) 0.2 CaSO dihydrate 0.9

EXAMPLE 7 4)z 4 98 Calgon 0.9 ZnSO, (36% Zn) 0.2 CaSO, dihydrate- 0.9

EXAMPLE-s 1 Percent (NHQ SQ, -l 9'8 Calgon -11 -l ZnSO (36% Zn) '1- .5 Caso dihydrate -1 055 -EXAMPIJE 9 (NH SO 98 Calgon 1 ZnSO (36% Zn) 1 EXAMPLE (NH )SO 96 Calgon 2.0 ZnSO "(36'% Zn) -1 1.0 CaSO dihydrate 1.0

EXAMPLE 11 (NH SO r 96 Sodium tripolyphosphate 2 ZnSO (36% Zn) 1 CaSO dihydrate 1 EXAMPLE 12 (NH4)ZSO4 'Calgon 2 ZnSO, (36% Zn) -1--- 2 Sodium sesquicarbonate -1 2 EXAMPLE 13 (NI- Q 80 97 Calgon 1 21150 (36% Zn) -1 1 Sodiummetasilicate 1 EXAMPLE 14 NaNO 99 Calgon 0J5 ZnSO, (36% Zn) 0.5

EXAMPLE 15 (NI- Q 80 97 Tetrasodium pyrophosphate 1 ZnSO, (36% Zn) 2 EXAMPLE 16 (NH SO 9O Calgon 5 ZnSO (36% Zn) 2.5 Calcium acetate monohydrate 2.5

EXAMPLE 17 NaNO 97.5 Calgon -1 0.5 Sodium tripolyphosphate 0,5 ZnSO (36% Zn) 1.5

EXAMPLE 18 NaNO 98 Sodium phosphate glass (rnol ratio Na O:P 'O =l.3:l) 1

21180 (36% Zn) l 1- 1 EXAMPLE 19 V NaNO -1; 1 98 Sodium phosphate glass 7 ZnSO, (36% Zn) l Mixtures of urea with sodium nitrate are effective =icetunes.

This application is a continuation-in-part of my applicationSerial No. 265,926 filed January 10, 1952, and now abandoned.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A non-corrosive composition for melting ice and snow under conditions whereby corrosion of steel and aluminum are or'dinarilycoricurrently encountered which composition consists principally of a'freezingpoint dc pressant selected from thegroup consisting of ammonium sulfate, urea, and sodium nitrate and at least 0.2 percent by weight of a water-soluble alkali-metal molecularly dehydrated phosphate and at least the chemical equivalent amount of a water-soluble salt, other than the chlorides, of a divalent metal selected from the group consisting of zinc, calcium, and strontium.

2. A non-corrosive composition for melting ice and snow which consists of from about percent by weight to about 99 percent by weight of a freezing point depressant selected from the group consisting of ammo nium sulfate, sodium nitrate and urea, and from about 1 percent to about 10 percent by Weight of an inhibitor mixture, said mixture comprising at least one water soluble alkali-metal molecularly dehydrated phosphate and at least a chemical equivalent amount of at least onexwater-solub le salt, other than the chlorides, of a 'divalent metal selected from the group consisting of zinc,

strontium, and calcium.

'3. An ice-melting composition which is non-corrosive "to both ferrous metals and aluminum which consists of from about 90 perc'entby weight to about 99.8 percent by weight of a freezingpoint depressant selectedfrom the "groupconsisting of ammonium sulfate, urea, and sodium nitrate and from about 0.2 percent to about 10 percent by weight of amixture of (a) alkali-metal polyphosphate and (b) i a water-soluble salt other than the chlorides; of

"a divalent metal selected from the group consisting of zinc, strontium, and calcium, said salt being present in an amount which is at least chemically equivalent to the amountofpolyphosphat'e.

4. An ice-melting. composition inhibited against corrosion of both steel and aluminum which consists of a 'mixtureofa freezingpbint depressant selected from the group consisting of urea, ammonium sulfate, and sodium nitrate and (a) atleast 0.2 percentby weight of a watersoluble sodium polyphosphate and (b) a water-soluble saltother than the chlorides; of a divalent metal selected from the group of metals consisting of zinc, calcium, and strontium, and (b) being present in an amount whichis at least the" chemical equivalent of (a).

'5. 'Amethod of melting ice and snow by means of a chemical composition which in aqueous solution is noncorrosive to both steel and aluminum, which comprises contactingthe-ice and snow with a freezing point depressant composition wherein about 90 percent to 99.8 percent by weight is a compound selected'from the group consisting of urea, sodium nitrate, and ammonium sulfate, and about 0.2 percent to 10 percent by weight is a mixture of (a) an alkali-metal water-soluble molecularly dehydrated phosphate and (b) a water-soluble salt; other than the chlorides, of a divalent metal selected from the group consisting of calcium, strontium, and zinc, the weight of (b) being at least the chemical equivalent of (a).

6. As a non-corrosive ice-melting composition suitable for use in :the presence of aluminum and steel, a mixture of about 98 percent by weight of ammonium sulfate,

about 1 percent Jay-weightofa water-soluble glassy molecularly dehydrated sodium phosphate having a mol ratio of Na O to P of about 1.1 to 1 and about 1 percent of zinc. sulfate.

7. As a non-corrosive ice-melting composition suitable for use in the presence of aluminum and steel, a mixture of about 98 percent by weight of a freezing point depressant consisting essentially of sodium nitrate and urea and about 1 percent water-soluble alkali-metal molecularly dehydrated phosphate, about one-half percent zinc sulfate, and about one-half percent calcium acetate monohydrate.

8. An ice-melting composition which when used in suflicient concentration to melt ice is relatively non-corrosive to both ferrous metalsand aluminum, said composition consisting of (a) urea from about 90 percent to about 99.8 percent by weight, (b) alkali-metal polyphosphate having a molar ratio of alkali-metal to phosphorus pentoxide of from about 0.7 to 1 to about 2 to 1, from about 0.2 percent to about 5 percent by weight, (c) water-soluble salt of a divalent metal selected from the group consisting of zinc sulfate, calcium acetate, and calcium sulfate, in an amount which is the chemical equivalent of (b).

9. An ice-melting composition as described in claim 8 wherein (a) is sodium nitrate.

10. An ice-melting composition as described in claim 8 where (a) is urea about 98 percent by weight, (b) is an alkali-metal polyphosphate having a molar ratio of alkali-metal to phosphorus pentoxide of from about 0.7

to 1 to about 2 to 1, about 1 percent by weight, and (c) is zinc sulfate about 1 percent by weight.

11. A method of melting ice and snow by means of a chemical composition which in aqueous solution is noncorrosive to both steel and aluminum, which comprises contacting the ice and snow with a freezing point depressant composition, wherein about percent to 99.8 percent by weight of which is a compound consisting of urea, and about 0.2 percent to about 10 percent by weight of which is a mixture of (a) an alkali metal watersoluble molecularly dehydrated phosphate and (b) a water-soluble salt other than chlorides of a divalent metal selected from the group consisting of calcium, strontium, and zinc, the weight of (b) being at least the chemical equivalent of (0).

References Cited in the file of this patent UNITED STATES PATENTS Eichengrun Apr. 28, 1936 Kaufman Nov. 15, 1938 Telkes May 4, 1954 FOREIGN PATENTS Italy Mar. 24, 1938 OTHER REFERENCES 

1. A NON-CORROSIVE COMPOSITION FOR MELTING ICE AND SNOW UNDER CONDITIONS WHEREBY CORROSION OF STEEL AND ALUMINUM ARE ORDINARILY CONCURRETLY ENCOUNTERED WHICH COMPOSITION CONSISTS PRINCIPALLY OF A FREEZING POINT DEPRESSANT SELECTED FROM THE GROUP CONSISTING OF AMMONIUM SULFATE, UREA, AND SODIUM NITRATE AND AT LEAST 0.2 PERCENT BY WEIGHT OF A WATER-SOLUBLE ALKALI-METAL MOLECULARLY DEHYDRATED PHOSPHATE AND AT LEAST THE CHEMICAL EQUIVALENT AMOUNT OF A WATER-SOLUBLE SALT, OTHER THAN THE CHLORIDES, OF A DIVALENT METAL SELECTED FROM THE GROUP CONDISTING OF ZINC, CALCIUM, AND STRONTIUM. 